ICMP 8 ICMP IP protocol number 1 Formats

ICMP 8강

ICMP • IP protocol number 1 • Formats: Fig. 8 -1, 8 -2 – TLV again: type, code, (checksum), payload • Type: big classification • Code: small classification – Checksum is Internet checksum

ICMP usages • IP datagram delivery failure notification – To source – Why: should be something that source can correct (otherwise, what’s the point? ) • Probing network state (“informational”) – Ping, tracert – Round-trip time, loss rate

ICMP usages • Table 8 -1, 8 -2 • Some notable ones – 3. 3, 3. 4, 3. 5, 5. 1, 8. 0, 8. 1, 11. 0

ICMP processing • Incoming – Informational: OS – Error: application or transport (TCP) • DF error TCP • Redirect OS : routing table update

ICMP errors • Explains to source why delivery failed there • Not generated for – ICMP error – Bad header (e. g. checksum error) – Multicast/broadcast – Invalid source addr (e. g. 0. 0) – Fragments other than the first

ICMP error • Carries a copy of the “offending” packet – i. e. the dead one – IP—ICMP—dead. IP • Dead IP = IP header + some payload – Contains transport number • At least 8 bytes of payload, now more – Find the culprit (application)!

ICMP redirect • When there are more than 2 routers on a subnet – One is default, the other’s not – What happens your packet went to default but should have gone to the other? • Redirect! • Packet is normally routed, however

Tracert • Windows uses ICMP Echo Request (8. 0) – Linux uses UDP • With high port numbers likely unused by normal processes – What’s good about using ping instead of UDP datagram? • Try www. monaco. edu from home – Not from KU (firewall …)

ICMP query/information msgs • Echo Request/Reply • Router Discovery – IPv 4: rare, used in Mobile IP – IPv 6: fundamental! -- ICMPv 6 • Neighbor Discovery (ND) • Multicast Listener Discovery (MLD) – later • All others by DCHP today

ping • Ping: target OS echoes – Sequence number – Identifier • Process ID in Linux

Neighbor Discovery (ND) in IPv 6 • ICMPv 6 = ICMP Router Discovery + ICMP Redirect + ARP in v 4 – Supports Mobile IPv 6 • Allow nodes on the same link – Find each other – Determine if they have bidirectional connectivity – Determine if a neighbor is unavailable – Supports stateless address autoconfig

ND • Two main parts – Neighbor Solicitation/Advertisement (NS/NA) • ARP, basically – Router Solicitation/Advertisement (RS/RA) • • Router discovery Mobile agents discovery Redirect Autoconfiguration • Hop Limit = 255

ICMPv 6 RS/RA • RA periodically – Sent to All Nodes multicast addr = ff 02: : 1 • Or unicast if in response to RS • RS induces RA – Sent to All Routers multicast addr = ff 02: : 2 – Flags • • M: should not use stateless addr autoconfig O: should not use stateless other autoconfig H: willing to act as a HA P: proxy ARP (experimental)

ICMPv 6 NS • Replaces ARP request – Sent to Solicited-Node multicast address corresponding to the target IPv 6 addr • ff 02: : 1: ff/104 • Can also be used for detecting – Nearby nodes can be reached – If they can be reached bidirectionally – Sent to the target unicast address

Solicited-Node multicast • Acts as a pseudo-unicast address for efficient address resolution – Fe 80: : 210: 18 ff: fe 00: 100 b ff 02: : 1: ff 00: 100 b 64 bits Unicast prefix Interface ID 24 bits FF 02: 0: 0: 0: 0 : 1: FF

ICMPv 6 NA • Replaces ARP response – In response to NS – Asynchronously when IPv 6 addr changes • Not a request! – Flags • R: I am a router • S: in response to a NS bidirectional connectivity! • O: override cache